1. Field of the Invention
The present invention relates to a centrifugal fan. In particular, the present invention relates to a method of manufacturing a housing component.
2. Description of the Related Art
Small and high-performance electronic devices, such as notebook PCs, produce a large amount of heat at CPUs and the like inside cases thereof. This makes it important to take measures against the heat. One common measure against the heat is to install blower fans inside the cases to discharge the heat. Meanwhile, there has been a demand for a reduction in thickness of the notebook PCs. Accordingly, the blower fans have been required to be reduced in thickness while reducing a deterioration in air-blowing performance.
A housing cover of a centrifugal fan disclosed in JP-A 2007-239712, for example, can be produced at a low cost by subjecting a thin plate material of stainless steel to press working. The housing cover includes a cover upper portion and a cover side wall portion. A small thickness of the cover is thereby easily accomplished, making it possible to achieve a reduction in thickness of the centrifugal fan. However, it is not easy to define a side wall portion and a plate portion as a single component by the press working. Accordingly, a method of manufacturing the plate portion and the side wall portion as a single component by a die casting process comes to mind.
When the die casting process is employed to produce a component including a portion in the shape of a thin plate, it is not easy to cause a molten metal to properly flow into a space in the shape of a thin plate in a mold. Accordingly, a variety of contrivances are required, as proposed by JP-A 2003-48047, JP-A 2002-160041, and so on, for example.
JP-A 8-90211 discloses a technique of producing a box structure of an electronic device by an aluminum die-casting process. A side plate and a bottom plate are integrally molded in the box structure. A sprue having a thickness greater than that of the bottom plate is defined at a portion of an edge of the bottom plate. No portion of the side plate is provided at an area where the sprue exists. The sprue having a relatively large thickness increases strength of the bottom plate. In addition, a shoulder portion is defined between the bottom plate and an injection sleeve to prevent an unwanted cut or deformation when a sprue gate is cut and removed after the casting is completed. Moreover, the sprue having a relatively large thickness enables a molten metal to flow easily, and contributes to improving quality of the box structure.
A plate portion of a housing is required to have an extremely small thickness in order to achieve a reduction in thickness of a centrifugal fan to be installed in a PC or the like. In addition, a side wall portion is arranged to connect with an outer edge portion of the plate portion over a large area. Therefore, when the plate portion and the side wall portion are to be molded as a single piece by a die casting process, a seam or an unwanted external appearance caused by a misrun tends to easily occur, making it hard to accomplish the molding easily. Meanwhile, since a channel for an air is defined inside the housing, the housing is required to have a shape that does not disturb an air current.